Telecommunication systems, cable television systems, and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting the signals over long distances with very little loss.
Optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmissions capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at disparate wavelengths. Maximum network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth, or size of the channels.
For metropolitan area networks, DWDM metro rings are the standard optical transport topology. A number of optical rings can be scaled together by interconnecting the rings at discrete nodes. When a lightpath is provisioned from an ingress node to an egress node, the data is transmitted and received at the ends by a corresponding pair of transponder cards. The transponder cards convert data signals between the optical network domain and an electrical client domain. Transponder cards also tune incoming client signals into an ITU-T specification wavelength. Transponder cards are generally optical-electrical-optical based wavelength readmitters. Transponder cards can cover partial operating bands.